Signaling system for voice and telegraph operation



March 2, 1937. E R, TAYLQR ET AL 2,072,227

SIGNALING SYSTEM FOR VOICE AND TELEGRAPH OPERATION Filed Oct. 18, 1935 0t .3600d l ,cera es DIL 400i?,

Zena/zend n10 ffl-ated. E .Re/Heater.

rvlmwea. Privacy evz'ce WMM.. u

`` transmission link.

Patented Mar. 2, 1937 `IJAJIENT oFF-ICE SIGNALING SYSTEM Foa vorol ANDTELE-` GRAPH OPERATION Edmund Randolph Taylor, Mount'Vernon, N. Y.,`

and DorenMitchell, Bound Brook, `N. J., lassignors to American Telephoneand `Telegraph Company, a corporation kof New York Application Gctober18, 1935, Serial No. 45,654

12 Claims.

This invention relates to a signaling system for voice and` fortelegraph operation and, more especially, to along two-wire channe suchas a radio or a"cab1e link 'with a long four-wire In particular, itrelates to improvements ina radio signaling system, such asatransatlantic link, connected to a four-wire circuit from remote `pointsto the radio stations and includesequipmentby which the system asafwhole maybe used in high quality speech signaling or may be adaptedfor another form of communication such as telegraphy.`

`Its object is to devise circuit 'arrangements in such a system whichwill permit ready change- 5 over from speech or voice signaling totelegraph signaling and, in particular, -to high frequency printingtelegraphy, or the reverse. A further object is to provide circuitarrangementsV which will be of high quality for voice comprising specialdevices for such purpose and yet providing for the elimination orlocking of these devices so far as they are not essential to telegraphicoperation.

Further fpurposes and a clearer understanding of the invention willappear from the following ,specication and accompanying drawing in whichFigure 1 is a circuit diagram of one end of such a system as mentionedabove and set up for transmitting voice signals, that is, set up foroutgoing speech. In this, as in other gures,

`many parts are shoWnin conventionalized form. Fig'. 2 is the samecircuit as Fig. 1 but in condition for receiving voice signals, that is,set up for incoming speech. Fig. 3 is the same circuit but withadditions necessary or desirable to adapt the system for alternative usefor voice or telegraphic signaling and Fig. 4 gives a list of legends toassist in the reading of the circuits.

In connection with the legends of Fig. 4 it o will be of assistanceinthe reading of the drawing to point` out that when the echo Suppressors`are .in the released position (as atV 22 and 23 of Fig. 2) a conductiveconnection through the suppressor is established and when in operatedVL@position (as at 22 and 23 of Fig. 1) this conductive connection isbroken, asby opening relay contacts or the electrical equivalent.Also'as `concerns the singing Suppressors when they are in releasedposition (as'at Il and l2 of Fig.

5K0 `-2-)jthe circuit connectionis opened but'when in "perated`-positiona conductive closure is made,

as by closing relay contacts or the electrical equivalent.

Referring to Fig. 1, there is shown a radio 5 'transmittingstation A anda radio receiving station B, these, in general, being quite widelyseparated. At the station A there is shown a box T indicating 'thatatthis transmitting station there is` included the usual and appropriateequipment for generating high frequency oscillations, Afor receiving themessage to Vbe transmitted and for modulating the high frequency withthis message andall such other equipment as would be appropriate at aradio transmitting station. Similarly, the'box R at station B representsthe receiving equipment comprising amplifiers, `de tectors and all otherapparatus appropriate to the reception'of radio signals.

It is desired to connect these radio stations with some remote point Dwhich may be some hundreds or Vthousands of `miles away and, in anycase, of such a distance as to require'special precautions in connectionwith the transmission system between D and the radio stations. For thispurpose, we desire to use a so-called fourwire circuit,that is, a systemin which the outterminating set N which would, in general, in-

clude the common so-called hybrid set. The well known connection fromthe terminating set N to the subscribers station is indicated `morefully in Fig. 3. The four-wire circuit at station D includes variousdevices for maintaining transmission on a high quality and a higheiciency basis, this'involving the use of special forms of amplifiers,attenuating devices, echo Suppressors, etc. as will be described infurther detail below. From station D, the long-distance line wouldiinallyreach the station C, not veryremote from the radio stations, andfrom this point the two circuits of the four-wire circuit wouldseparate, one going lto stationA and the other tos'tation B.

`The circuit of Fig. '1 is set up on therbasis of outgoing speechandgwill now be described in that connection. Outgoing speech comingfrom the terminating set Nj passes into al vogad V which is an amplifierof such 'gain characteristic that it 4delivers speech of constant volumealltnoughthe incoming s'peechffrom the terminating set may be of widelydifferent loudness or volume. Such a device, now well known inthe art,is "described in jtheV patent to,v Hogg and Doba, No. 1,853,9'74, April12, 1932. Thetranstransmission circuit. The line, however, is enabled orestablished for transmission by means of speech, for speech at theoutput of the vogad V enters the amplifier-detector system I3 and theoutput thereof operates or closes the suppressors II and I2, thusenabling or establishing the circuit during the period and only duringthe period when speech is to be transmitted. At station D, there is anoscillation-generator I4, here shown for illustrative purposes as beingof a frequency of 3500 cycles and, in general, being of a frequencywhich is near but outside and, preferably, above the frequency of thespeech message to be transmitted. Normally, this generator is sending3500 cycles out over the line to the stations A and B to disable thetransmission path and enable the receiving path in a manner to behereinafter described. A portion of the output of the amplifier-detectorI3, however, disconnects the oscillator I4 by means of the echosuppressor I 5 during actual transmission of speech. In order to allowtime for the enablement of the transmission path, a transmission delaydevice I6 is introduced, as shown. Also, in the event that secrecy is tobe introduced by such a means as the shifting of frequency bands thenthe transmission path from I I passes through the secrecy or privacyequipment P to the point I2, whereupon it is impressed on thetransmission line going to the station C. This transmission path from Dto C may be many hundreds of miles long and it is to be understood,therefore, that suitable stations for repeaters, equalizers and similarequipment will be provided.

At the station C, the speech message is shown as passing through arepeater I'I from whence it may go another considerable distance to thevstation A. At the station A, it willnd the echo ysuppressor I9 releasedto permit passage of the message to the transmitting equipment T. Duringthis period, the receiving line is shown as interrupted at two points 22and 23 by echo suppressors which are operated from the amplierdetectorI3 Whenever the outgoing speech is present. The receiving line is alsointerrupted at the receiver R by the singing suppressor 25 in a mannerto be now described.

Normally, and when there is no outgoing speech, theoscillation-generator I4 is connected to the line through the suppressorI5 and the high-pass filter I-I. At the station C, this 3500- cyclecurrent divides; a portion of it goes to the station A and passingthrough the high-pass filter to the amplifier-detector 20 operates theecho suppressor I9, thus keeping the transmission path disabled as longas 3500-cycle current is present. A portion of the 3500-cycle currentalso passes across to the receiving path at the station C and istransmitted through suitable high-pass filters to the station B where itis impressed on the amplifier-detector 2| to maintain the singingsuppressor 25 in operated condition, thus enabling the receiving path atthis point as long as 3500- cycle current is present. It will thus beseen that when the outgoing speech disconnects the generator I4, theSuppressors I9 and 25 are both released, thus enabling the transmissionpath and disabling the receiving path.

In Fig. 2, the same circuit is shown but set up for the condition ofincoming speech. In this case, the 3500-cycle generator I4 is connectedto .the line and thereby operates the suppressor I9 in the transmissionpath and operates the suppressor 25, thus enabling the receiving path.The incoming message will then pass through suitable repeaters andfilters to the station C and on t6 the station D where it will nd theSuppressors 22 and 23 released. If the message has been subjected toprivacy band shifting, it will then pass through the privacy system P torestore the message to normal condition. The message will also actthrough the amplifier-detector 26 to operate the echo suppressor 2l,thus preventing the amplifier-detector I3 from exercising the controldescribed heretofore. The message will also pass through a variable lossdevice L which is set automatically or by hand to introduce a losswhich, in general, would be increased as the gain of the vogad, Vincreases and by such an amount as to prevent operation of amplifierdetector I3 by echoes of waves which were too weak to operateamplifier-detector 26. From this point, the received message passesthrough appropriate ampliers and out to the subscriber set.

At times, it is desirable to transmit over this circuit another type ofmessage such as printing telegraph, the circuit requirements for whichare substantially different than that for voice signals. Accordingly, weprovide for the rearrangement of the circuit of Figs. 1 and 2 as shownin Fig. 3, in order to enable ready transfer from the one form ofsignaling to the other. The sending telegraph source 28 may be of avariety of forms. It may, for example, be of a form which sends outgroups of oscillations of any suitable frequency such as 2,000. Uponplugging in the sending telegraph circuit at the terminating set N asuitable contact may be made, as through the sleeve connection 30,whereby current of suitable form, such as a d. c. current from battery3|, will be transmitted out to various points at the station D toperform certain functions. Thus, as shown in the figure, current passesdirectly over conductor 32 to the Suppressors II and I2 to keep themoperated, thus enabling the transmission circuit as long as the sleevecircuit is closed and also to operate Suppressors 22 and 23 thusdisabling transmission at these points. This sleeve current alsooperates the echo suppressor I5, thus disconnecting the 3500-cyclegenerator. The sleeve circuit also operates on the privacy system P toshort-circuit it or to replace it by some passive network of a lossequivalent to that introduced by the privacy system, as indicated at thepoint 33. In addition, the sleeve circuit operates on the vogad as shownat 34 to lock this device at a xed and appropriate gain; for it willobviously not, in general, be necessary, in the case of telegraphsignals, to have variable gain as is the case for speech signaling.Finally, the sleeve circuit operates suppressor 35 to connect in placeof the 3500-cycle generator a generator G2 of some other frequency suchas 4000 cycles. This 400G-cycle passes to the station C and thence tothe stations A and B. At the station A, it performs no function on theamplifier-detector 20 because of the introduction of a band-pass filter36. Thus, the 400G-cycle current cannot disable the transmission path atthe point I9. At the station B, however, the amplifier-detector 2Ioperates on both 3500 cycles and 4000 cycles and thus keeps thereceiving line closed at the point 25. Under these circumstances, itwill be seen that the 'circuit is in condition for transmission of thetelegraph message as long as the sending telegriaph equipment is pluggedin at the terminating se N.

Also, the receiving side of the circuit is in condition for reception ofsimilar telegraph message at al1 times so that transmission andreceppurpose of this invention, the receiving telegraph circuit, asshown in Fig. 3, derives from the main transmission channel at thestation D at the point 37 before it reaches echo suppressor 22 andother"equipment particularly appropriate for the voice message. For thisreason, it is desirable, as shown in Fig. 3, that the sleeve circuit 32shall operate the echo Suppressors 2-2 and 23 to open the transmissionpaths at these points. From point 31, the received telegraph message mayproceed to any appropriate receiving set 38. It will, of coursebeunderstood that the transmission of telegraph message from the far endof the radio link will be on a modulating frequency such as 1,000,sufficiently different from that used for transmission from the stationD to facilitate discrimination between the two by means of filters.Thus, for example, in order to make such discrimination more effectivethere is shown at the station B a band-pass filter 39 which passes theincoming telegraph frequency of, say, 1000 cycles. During the time ofvoice signaling, this band-pass lter should be eliminated and to thisend an amplifier-detector 40 is provided which passes 4000 cycles onlyand, upon establishment `of condition for telegraphy introduces thebandpass filter 39 and upon the establishment of condition for voicesignaling, the band-pass filter is shorted at the point 4 l When it is,desired to change from telegraphic to voice signaling, the sendingtelegraph equipment 30 is disconnected, whereupon the sleeve contact isalso broken. The source of speech message 52 may then be plugged inwhereupon the circuit is prepared for voice signaling.

It will be noted that during voice signaling the oscillation generatorof 3500 cycles performs a very important function. It sometimes occursthat, in the event of strong speech, there may be generated harmonics ofcertain of the speech frequencies which lie at orr very close to thefrequency of 3500 cycles and may, therefore, occasionally operate thesuppressor, thus disabling the transmission path, and may also operatethe suppressor 25, thus enabling the receiving path at a time when itshould remain disabled. To avoid this diiiiculty, we may provide anadditional suppressor 4E which is operated by speech to disable at thepoint 46, the circuit leading from the amplifier-detector 20. Also atthe station C, a circuit derived from the transmission side through theband-pass filter 47 and amplifier-detector 48 operates on speech aloneto disable at the point 49 the circuit leading from the transmission tothe receiving side, thus preventing false operation of the suppressor 25by outgoing speech.

It is apparent that the description given above is quite specific forthe purpose of making the invention more clear but it is equallyapparent that many variations may be made without departing from thespirit of our invention.

What is claimed is:

1. In a carrier frequency signaling system adapted for speech signalingoperation and telegraph signaling operation with different circuitconnections, a transmitting channel and a receiving channel, meanswhereby during the speech operation one channel is always disabled andthe other channel enabled, means at one point for disconnecting thespeech source and connecting a source of telegraph signals, and acontact at the same point controlled thereby to rearrange the circuitfor telegraph operation.

2. The combination of claim 1 characterized bythe fact that when thecircuit is rearranged "for telegraph operation, both transmitting andreceiving channels are enabled.

13. In fa 'carrier frequency signaling system adapted'for speechsignaling operation and telemaintains the transmission channel `disabledand` the receiving channel enabled, means for substituting a source oftelegraph signals for the speech source, and a contact controlledthereby to rearrange the circuit for telegraph operation.

4. The combination of claim 3 characterized by the fact that when thecircuit is rearranged for telegraph operation, both transmitting andreceiving channels are maintained in an enabled condition.

5. In a carrier frequency signaling syste adapted for voice signalingoperation and telegraph signaling operation with different circuitconnections, a transmitting and a Vreceiving channel, means which duringvoice operation normally maintains the transmitting channel disabled andthe receiving channel enabled and which on transmission of voice permitsenablement of the transmitting channel and disablement of the receivingchannel, means at one point for disconnecting the speech source andconnecting a source of telegraph signals, and a contact at the-samepoint controlled thereby to rearrange the circuit for telegraphoperation.

6. The combination of claim 5 characterized by the fact that when thecircuit is rearranged for telegraph operation, both transmitting andreceiving channels are enabled.

'7. In a carrier frequency signaling system adapted for voice signalingoperation and telegraph signaling operation with dilerent circuitconnections, a transmitting channel and receiving channel, anoscillation generator and means whereby during voice operation itnormallymaintains the transmitting channel disabled and the receivingchannel enabled, a second oscillation generator of different frequencywhich, on telegraph operation, replaces the first oscillation generatorto maintain the telegraph circuit connections.

8. In a radio signaling system adapted for speech transmission andtelegraph transmission requiring different circuit arrangements, a radiotransmitting station and a radio receiving station, a long-line wirecommunication circuit from a remote point to said stations with atransmitting channel to the radio transmitting station and a receivingchannel from the receiving station, a speech signaling source and atelegraph signaling source, circuit enabling and disabling devices ineach wire channel at the remote point and in each channel at `the radiostations, meansk at the remote point and inserted in the two channels toestablish high eiiiciency transmission for speech signaling, means atthe remote point for substituting the source of telegraph signals forthe speech source and for locking or voiding the high efficiency meansnot required for telegraphy during telegraph operation.

9. The combination of claim 8 characterized by the fact that the meansinserted in the channels to establish high efficiency transmissioncomprises echo Suppressors, amplifiers and a vogad.

10. The combination of claim 8 characterized by the fact that when thecircuit is rearranged 10 cillation generator of a diierent frequencywhereby both channels at the radio stations are enabled. y 12. Thecombination of claim 8 characterized by the fact that a sleeve circuitconnection at th point of substitution of the telegraph source for thespeech source sets in motion the train of circuit changes to transferfrom speech connection to telegraph connection.

EDMUND RANDOLPH TAYLOR.

DOREN MITCHELL.

